Introduction

This module provides wrappers for the System V IPC family of functions.
It includes semaphores, shared memory and inter-process messaging (IPC).

Semaphores may be used to provide exclusive access to
resources on the current machine, or to limit the number of
processes that may simultaneously use a resource.

This module provides also shared memory functions using System V
shared memory. Shared memory may be used to provide access to
global variables. Different httpd-daemons and even other programs
(such as Perl, C, ...) are able to access this data to provide a
global data-exchange. Remember, that shared memory is NOT safe
against simultaneous access. Use semaphores for synchronization.

Limits of Shared Memory by the Unix OS

SHMMAX

max size of shared memory, normally 131072 bytes

SHMMIN

minimum size of shared memory, normally 1 byte

SHMMNI

max amount of shared memory segments on a system,
normally 100

SHMSEG

max amount of shared memory segments per process, normally 6

The messaging functions may be used to send and receive messages to/from
other processes. They provide a simple and effective means of exchanging
data between processes, without the need for setting up an alternative
using Unix domain sockets.